1. Field of the Invention
The present invention relates to a heat energy recovery apparatus for converting thermal energy in which heat is absorbed by a heat exchanger to mechanical energy.
2. Description of the Related Art
Conventionally, there exists a heat cycle engine that converts thermal energy to mechanical energy.
For example, as this kind of a heat cycle engine, there is a Brayton cycle engine which includes a compressor which adiabatically compresses sucked-in working fluid (working gas), a heat exchanger which makes the working gas adiabatically compressed by the compressor absorb heat of high temperature fluid under isobaric pressure, and an expander which makes the working gas isobarically heat-received by the heat exchanger expand adiabatically; and which takes out output from a crankshaft using the expansion force, as disclosed in Japanese Patent Application (JP-A) Laid-Open No. 6-257462.
As described, the heat cycle engine is to obtain output using expansion force of heated working gas and, for example, is able to construct as an exhaust heat recovery apparatus (heat energy recovery apparatus) for an internal combustion engine by using exhaust heat of exhaust gas of the internal combustion engine.
Furthermore, as such a heat cycle engine, there is a Stirling cycle engine in which heating from outside to a cylinder sealed with working fluid (working gas) and cooling of working gas expanded by this heating are repeated; and depressing of a piston due to expansion force of the working gas increased in temperature and ascending of the piston due to cooling of the expanded working gas are repeated, thereby taking out output from a crankshaft, as disclosed in JP-A No. 2002-266701.
However, in the aforementioned heat cycle engine, if the engine works regardless that required engine output is low, output taken out with the work wastes, resulting in bringing degradation in recovery efficiency of thermal energy.
Furthermore, in the heat cycle engine such as the aforementioned Brayton cycle engine, each volume of the compressor and an expander is determined on the assumption that the working gas can sufficiently receive heat. For this reason, if the Brayton cycle engine works when heat receiving capacity of the working gas is small, such as in the case there is no heat or extremely low in heat in the heat exchanger, pumping loss is generated in the expander. Then, the compressor continues to generate compressed working gas in vain regardless of generating such a pumping loss, resulting in degradation in recovery efficiency of thermal energy.